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Modbus RTU Exception Codes
Introduction
36 HC900 Hybrid Controller Communications User Guide Revision 4
9/03
Table 5-1 Modbus RTU Data Layer Status Exception Codes
Exception
Code
Definition Description
01 Illegal Function The message received is not an allowable action for
the addressed device.
02 Illegal Data Address The address referenced in the function-dependent data
section of the message is not valid in the addressed
device.
03 Illegal Data Value The value referenced at the addressed device location
is not within range.
04 Slave Device Failure The addressed device has not been able to process a
valid message due to a bad device state.
06 Slave Device Busy The addressed device has rejected a message due to
a busy state. Retry later.
07 NAK,
Negative Acknowledge
The addressed device cannot process the current
message. Issue a PROGRAM POLL to obtain device-
dependent error data.